WO2013133851A1

WO2013133851A1 - Multi-stable electronic inks

Info

Publication number: WO2013133851A1
Application number: PCT/US2012/028609
Authority: WO
Inventors: Qin Liu; Zhang-Lin Zhou; Gregg Combs
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2012-03-09
Filing date: 2012-03-09
Publication date: 2013-09-12
Also published as: TW201348347A

Abstract

A multi-stable electronic ink is disclosed. The multi-stable electronic ink includes a non-polar carrier fluid, a colorant particle, and an oligomer having a number average molecular weight between 183 and 20,000, exclusive.

Description

MULTI-STABLE ELECTRONIC INKS

BACKGROUND

[001] Ultrathin, flexible reflective electronic displays that look like print on paper are of great interest as they have potential applications in wearable computer screens, electronic paper, smart identity cards, and electronic signage. Electro-optical display technology, such as electrophoretic or electrokinetic display technology, is an important approach to this type of display medium. In electrophoretic or electrokinetic displays, pixel or segment electrodes, electrodes within the viewing area of a display that are electrically isolated, may control the local position of charged colorant particles in the ink by application of electric fields. The local position of the particles may influence the reflectance of such pixel or segment electrodes. Without subscribing to any particular theory, in electronic inks, particles that exhibit good dispersibility and charge properties in non-polar dispersing media may increase the stability of the ink, may improve the switching behavior of the ink, and may give the ink multi- stability properties, as further discussed below. Additionally, use of non-polar dispersing media in the electrophoretic or electrokinetic devices may minimize current leakage.

[002] As noted previously, electrophoretic and electrokinetic displays may have numerous applications. Some display applications, such as e-books and other digital signage applications, do not require updates at the same rate as video display applications. In one example, instead of an update rate measured in fractions of a second, the information displayed in an e-book or another digital signage application may require an update anywhere from every few seconds to once a day or once every few days. Therefore, if a display does not require constant power to maintain images, it may consume less power when displaying images, which may result in power savings and a device that may be more easily remotely deployed. BRIEF DESCRIPTION OF THE DRAWINGS

[003] The detailed description will make reference to the following drawings, in which like reference numerals may correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals having a previously described function may or may not be described in connection with other drawings in which they appear.

[004] FIG. 1 depicts a cross-sectional view of one example of a stacked electro-optical display including an ink with the oligomer disclosed herein.

[005] FIG. 2, on coordinates of relative intensity and time, illustrates the intensity of the light state over a set period of time of an electrokinetic device removed from power and including electronic inks with a magenta pigment and varying amounts of the oligomer disclosed herein.

[006] FIG. 3, on coordinates of relative intensity and time, illustrates the intensity of the light state over a set period of time of an electrokinetic device removed from power and including electronic inks with a black pigment and varying amounts of the oligomer disclosed herein.

[007] FIG. 4 is a depiction of an image displayed in an electrokinetic device using an electronic ink including the oligomer described herein 40 minutes after the electrokinetic device has been removed from the power source.

[008] FIG. 5A is a depiction of an image displayed in an electrokinetic device using an electronic ink including the oligomer described herein and connected to a power source.

[009] FIG. 5B is a depiction of an image displayed in the electrokinetic device of FIG. 5A 15 hours after the electrokinetic device has been disconnected from a power source. DETAILED DESCRIPTION

[0010] Reference is now made in detail to specific examples of the disclosed oligomer and specific examples of multi-stable electronic inks including such oligomers. When applicable, alternative examples are also briefly described.

[0011] It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0012] As used in this specification and the appended claims, "about" means a ± 10% variance caused by, for example, variations in manufacturing processes.

[0013] As used herein, the "carrier fluid" is a fluid or medium that fills up a viewing area defined in an electronic ink display and is generally configured as a vehicle to carry colorant particles therein.

[0014] Multi-stable or low power reflective color displays or multi-stable displays may be distinguished from traditional displays, such as liquid crystal displays (LCDs), because after a multi-stable display is removed from the power source, the image displayed will remain displayed until power is restored to the device and the image is updated (i.e. changed). Accordingly, "multi-stability" refers to the ability of the device, after removal from power, to maintain two or more states. As applied to an ink, "multi-stability" refers to the ability of the ink to help achieve the multiple states in the device. In multi-stable devices capable of two states, such states appear on the device as a maximum color-saturated state, sometimes known as the "dark state," and a minimum color-saturated state, sometimes known as the "clear state," wherein the minimum and maximum levels of saturation are determined by the specifications of the device. In multi-stable devices including more than two states, there may be one or more additional different colored states, each state independently having a different level of color saturation between the maximum color-saturated state and the minimum color-saturated state. [0015] Accordingly, multi-stable or low power displays may be desirable in applications such as e-book readers and signage applications that may not require as many image updates as a video display. For example, often, an active display may be a large power-consuming component in a portable device. Therefore, in some portable devices, such as e-books or other signage displays where images may remain static for long periods of time, use of multi-stable displays may allow power to be turned off and conserved during such static times, which may result in a device with a longer battery life.

[0016] In some examples, a multi-stable display may be an electrokinetic device or other electro-optical device that includes multi-stable inks. Such a display, as discussed above, may require only the power necessary to change the image displayed, with no additional power required to maintain the image. In contrast, electrokinetic displays using other inks, such as non-multi-stable inks, may require complex driving schemes for maintaining gray scale control and the static images, which may result in the device requiring more power to achieve the same functions as a multi-stable device. Additionally, use of multi-stable inks may allow for the use of passive matrix devices that use patterned electrodes in the viewing area instead of active matrix devices. Active matrix devices may use more complicated transistors at each pixel, and may thereby be more complex and costly to manufacture. Therefore, using multi-stable electronic inks in electrokinetic devices may result in devices with simplified driving schemes and low power consumption, which may result in power savings, cost savings, and devices with a longer battery life.

[0017] However, multi-stable inks are difficult to create as the mechanisms for multi-stability are not well understood. For example, current commercial multi-stable displays, such as displays manufactured by prior art display technology companies, utilize front to rear particle motion, which may only be able to provide opaque color and white states or black and white states. Additionally, such displays may not be capable of producing the clear states that allow displays to be used in stacked architectures, as further described below, and may rely on color filters to achieve full color. However, color filters, such as red, green, and blue filters, may often be arranged side-by-side in a pixel, which may result in a decreased surface area within the pixel for modulating light and a decreased surface area within the pixel for reflecting incident light when not all of the color filters are required to produce a color. Accordingly, the resulting displayed image using color filters may have duller colors.

[0018] The ability to achieve a clear state, on the other hand and as further described below, may allow displays to sit in a stacked architecture, which allows the entire viewable area in the display to be used (i.e. the entire pixel of every pixel) when modulating light and reflecting incident light, which may result in the display achieving brighter colors and a better light state. Additionally, because the entire viewable area in the display may be used to modulate light, such displays may also have a larger color gamut volume.

[0019] In the past, Hewlett-Packard has conducted research on displays utilizing electrokinetic architecture that rely on pigment compaction, which permits both a colored state when the colorant particles are spread out and a clear state when the particles are tightly compacted within a cell or pixel, and wherein the repeated motion of spreading out and compacting is known as "switching". (See e.g., Yeo, J. et al., "Electro-optical Display", US Patent 8,018,642). However, inks currently used in prior art displays may not work in stacked versions of the electrokinetic architecture as such inks may be unable to achieve the level of compaction necessary to provide the clear states used in displays with stacked color architectures, as further described below. Accordingly, researchers continue to develop electronic inks for such stacked architectures by conducting research on and improving the conventional stabilization techniques and materials used in multi-stable inks. (See e.g., Zhou, Z. L. et al., "Electronic Inks" published on April 21 , 2011 as WO201 1/046562; Zhou, Z. L. et al., "Dual Color Electronically Addressable Ink" published on April 21 , 201 1 as WO201 1/046564; and Zhou, Z. L. et al., "Electronic Inks" published on April 21 , 201 1 as WO201 1/046563.) [0020] A new multi-stable electronic ink for low power electrophoretic or electrokinetic displays is disclosed, wherein the new multi-stable electronic ink includes an oligomer having a number average molecular weight (M_n) between 183 and 20,000, exclusive. As used herein, in a numerical range, "exclusive" means not including the numerical values explicitly recited as the limits of the range. For example, a value between "1 and 10, exclusive" means any numerical value between 1 and 10 except for 1 and 10.

[0021] While multi-stable electronic inks including polymers have been studied in the past, such studies have focused on non-absorbing higher molecular weight polymers, such as those with a M_n greater than 20,000 and often times greater than 100,000. The multi-stable electronic ink disclosed herein includes a lower weight oligomer, i.e. having a M_n between 183 and 20,000, exclusive. Without subscribing to any particular theory, it appears that the use of lower weight oligomers in an electronic ink may allow the electronic ink to achieve multi-stability due to a balance of forces between the ink particles, including repulsion, attraction, and other forces, while maintaining switchability. Additionally, there is a broader range of materials suitable for use as a low molecular weight oligomer additive in an electronic ink than as a higher weight polymer additive in an electronic ink, as oligomer and polymer solubility in non- polar media may be dependent on the molecular weight of the oligomer or polymer. Since lower molecular weight oligomers and polymers are more soluble, there may be more lower weight oligomer or polymer materials that are compatible with the non-polar media used in electronic inks than there are compatible higher weight oligomers and polymers.

[0022] FIG. 1 illustrates a cross-sectional view of one example of a stacked electro-optical display 100 including an ink with the oligomer described herein. The electro-optical display 100 includes a first display element 102a, a second display element 102b, and a third display element 102c. The third display element 102c is stacked on the second display element 102b, and the second display element 102b is stacked on the first display element 102a. Turning now to electronic inks 120, 122 that employ the oligomers disclosed herein, examples of such electronic inks may generally include a non-polar carrier fluid 120, a pigment particle 122, the oligomer described herein, and other additives, such as surfactants, dispersants or charge directors.

[0023] In some examples, each display unit includes a first substrate 104, a first electrode 106, a dielectric layer 108 including reservoir or recess regions 1 10, thin layers 1 12, a display cell 1 14, a second electrode 1 16, and a second substrate 1 18. In other examples, the display unit does not include thin layers 1 12. The display cell 1 14 may be filled with the electronic ink 120, 122 disclosed herein including a carrier fluid 120 with colorant particles 122. In some examples, wherein thin layers 1 12 are included, the thin layers 112 may be opaque. In other examples, the thin layers 1 12 may be transparent. In examples wherein thin layers 1 12 are included, the thin layers 1 12 may include dielectric materials or conductive materials. In one specific example, a metallic material, such as nickel, may be used.

[0024] In examples wherein thin layers 1 12 are included, the first display element 102a includes thin layers 1 12a self-aligned within the recess regions 1 10. The first display element 102a also includes colorant particles 122a having a first color (e.g., cyan) for a full color electro-optical display. The second display element 102b includes thin layers 1 12b self-aligned within the recess regions 1 10. The second display element 102b also includes colorant particles 122b having a second color (e.g., magenta) for a full color electro-optical display. The third display element 102c includes thin layers 1 12c self-aligned within the recess regions 1 10. The third display element 102c also includes colorant particles 122c having a third color (e.g., yellow) for a full color electro-optical display. In other examples, colorant particles 122a, 122b, and 122c may include other suitable colors for providing an additive or subtractive full color electro- optical display.

[0025] In the example illustrated in FIG. 1 , in the electro-optical display 100 including the electronic ink disclosed herein 120, 122, the first display element 102a, the second display element 102b, and the third display element 102c are aligned with each other. As such, the thin layers 1 12a, 1 12b, and 1 12c are also aligned with each other. In this example, since the recess regions 1 10 and the self-aligned thin layers 112a, 1 12b, and 112c of each display element 102a, 102b, and 102c, respectively, are aligned, the clear aperture for the stacked electro-optical display 100 may be improved as compared to a stacked electro-optical display without such alignment.

[0026] In an alternate example (not shown), the first display element 102a, the second display element 102b, and the third display element 102c may be offset from each other. As such, the thin layers 1 12a, 112b, and 1 12c are also offset from each other. In this example, since the recess regions 1 10 and the self-aligned thin layers 1 12a, 1 12b, and 1 12c are just a fraction of the total area of each display element 102a, 102b, and 102c, respectively, the clear aperture for the stacked electro-optical display 100 may remain high regardless of the alignment between the display elements 102a, 102b, and 102c. As such, the process for fabricating the stacked electro-optical display 100 may be simplified. The self-aligned thin layers 1 12a, 1 12b, and 1 12c may prevent tinting of each display element due to the colorant particles 122a, 122b, and 122c, respectively, in the clear optical state. Therefore, a stacked full color electro- optical display having a bright, neutral clear state and precise color control may be provided.

[0027] Turning now to electronic inks that employ the oligomers described herein and may be used in the electro-optical displays described above, such as electrokinetic displays, examples of such electronic inks may generally include the oligomer described herein, a non-polar carrier fluid 120, a colorant or pigment particle 122, and other additives, such as other surfactants, dispersants or charge directors.

[0028] As discussed above, the use of a new additive in electronic inks is disclosed, wherein the new additive is an oligomer having a M_n of between 183 and 20,000, exclusive. In some examples, the oligomer may have a base of any hydrocarbon monomer or siloxane. Specific examples of the disclosed oligomer may include, but are not limited to, polyisobutylenes, polybutenes, polyesters, polyvinyls, polyacrylates, polymethacrylates, polystyrenes or poly(dimethylsiloxane)s. Also, in some examples, the oligomer may further include one or more functional groups including, but not limited to, acrylates, alcohols, amides, amines, carbamates, carboxylates, epoxies, esters, ethers, guanidiniums, imines, ketones, oximes, phosphates, phosphonates, protonated nitrogens, siloxanes, sulfates, sulfonamides or combinations thereof. Such functional groups may allow the ink to have further functionalities or improve various properties of the ink.

[0029] In some examples, the carrier fluid may act as a vehicle for dispersing the pigment particle and may act as an electrokinetic or electrophoretic medium. In one example, non-polar fluids are used, as such fluids may reduce leakages of electric current when driving the display and may increase the electric field present in the ink. In some examples, the non-polar carrier fluid may be a fluid having a low dielectric constant k such as, e.g., less than about 20 or, in some examples, less than about 2. In response to a sufficient electric potential or field applied to the colorant particles while driving electrodes in the display, the colorant particles may move or rotate to different spots in the area of the display viewable by a user to produce different images. In other examples, carrier fluids may also vary with respect to viscosity, resistivity, specific gravity, chemical stability, or toxicity, and in other examples, such differences may be considered when formulating an electronic ink. For example, a carrier fluid that is too viscous may slow down the spread or compaction of the colorant particles, which may affect the switching speed and may result in a less effective electronic ink.

[0030] Specifically, in some examples, the non-polar carrier fluid may include one or more fluids selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, oxygenated fluids, siloxanes, and combinations thereof. Some specific examples of non- polar carrier fluids may include, but are not limited to, perchloroethylene, cyclohexane, dodecane, mineral oil, isoparaffinic fluids, cyclopentasiloxane, cyclohexasiloxane, cyclooctamethylsiloxane or combinations thereof.

[0031] In some examples, pigment or colorant particle added to electronic inks may provide color and charge to the electronic ink. Similar to the carrier fluid in the ink, different pigment or colorant particles may have different characteristics, such as different sizes, dispersibility properties-, hues, colors, or lightness. Additionally, different pigment particles may be further functionalized to contain different functional groups, which may further vary properties of the particle, including, but not limited to, hydrophilicity and hydrophobicity, acidity and basicity, or density of the particles.

[0032] The pigment particle may be a colored pigment or colored polymeric particle in any possible color, such as RGB or CYMK, with a size ranging from 10 nm to 10 pm. In some examples, smaller particles, with a particle size from 1 to 10 nm, such as quantum dots, may be employed. In other examples, the particle size may range to a few micrometers. Additionally, organic or inorganic pigments may be used.

[0033] Organic and inorganic pigment particles may be selected from black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles or white pigment particles. In some instances, the organic or inorganic pigment particles may include spot-color pigment particles, which are formed from a combination of a predefined ratio of two or more primary color pigment particles.

[0034] A non-limiting example of a suitable inorganic black pigment includes carbon black. Examples of carbon black pigments include those manufactured by Mitsubishi Chemical Corporation, Japan (such as, e.g., carbon black No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100 or No. 0B); various carbon black pigments of the RAVEN^® series manufactured by Columbian Chemicals Company, Marietta, Georgia, (such as, e.g., RAVEN 5750, RAVE 5250, RAVEN 5000, RAVE 3500, RAVEN 1255 or RAVEN® 700); various carbon black pigments of the REGAL® series, the MOGUL® series or the MONARCH® series manufactured by Cabot Corporation, Boston, Massachusetts, (such as, e.g., REGAL® 400R, REGAL® 330R, REGAL® 660R, MOGUL® L, MONARCH® 700, MONARCH® 800, MONARCH® 880, MONARCH^® 900, MONARCH ^® 1000, MONARCH® 1 100, MONARCH® 1300 or MONARCH® 1400); or various black pigments manufactured by Evonik Degussa Corporation, Parsippany, New Jersey, (such as, e.g., Color Black FW1 , Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, PRINTEX® 35, PRINTEX^® U, PRINTEX® V, PRINTEX^® 140U, Special Black 5, Special Black 6A or Special Black 4). A non-limiting example of an organic black pigment includes aniline black, such as C.I. Pigment Black 1 .

[0035] Other examples of inorganic pigments include metal oxides and ceramics, such as the oxides of iron, zinc, cobalt, manganese or nickel. Non- limiting examples of suitable inorganic pigments include those from the Shepherd Color Company (Cincinnati, OH) such as Black 10C909A, Black 10P922, Black 1 G, Black 20F944, Black 30C933, Black 30C940, Black 30C965, Black 376A, Black 40P925, Black 41 1A, Black 430, Black 444, Blue 10F545, Blue 10G51 1 , Blue 10G551 , Blue 10K525, Blue 10K579, Blue 21 1 , Blue 212, Blue 214, Blue 30C527, Blue 30C588, Blue 30C591 , Blue 385, Blue 40P585, Blue 424, Brown 10C873, Brown 10P835, Brown 10P850, Brown 10P857, Brown 157, Brown 20C819, Green 10K637, Green 187 B, Green 223, Green 260, Green 30C612, Green 30C654, Green 30C678, Green 40P601 , Green 410, Orange 10P320, StarLight FL 37, StarLight FL105, StarLight FL500, Violet 1 1 , Violet 1 1 C, Violet 92, Yellow 10C1 12, Yellow 10C242, Yellow 10C272, Yellow 10P110, Yellow 10P225, Yellow 10P270, Yellow 196, Yellow 20P296, Yellow 30C119, Yellow 30C236, Yellow 40P140 or Yellow 40P280.

[0036] The following is a list of organic pigments that may be treated in accordance with the teachings herein. Non-limiting examples of suitable yellow pigments include C.I. Pigment Yellow 1 , C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 4, C.I. Pigment Yellow 5, C.I. Pigment Yellow 6,

C.I. Pigment Yellow 7, C.I. Pigment Yellow 10, C.I. Pigment Yellow 1 1 , C.I.

Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I.

Pigment Yellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 24, C.I.

Pigment Yellow 34, C.I. Pigment Yellow 35, C.I. Pigment Yellow 37, C.I.

Pigment Yellow 53, C.I. Pigment Yellow 55, C.I. Pigment Yellow 65, C.I.

Pigment Yellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I.

Pigment Yellow 81 , C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I.

Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I.

Pigment Yellow 98, C.I. Pigment Yellow 99, C.I. Pigment Yellow 108, C.I.

Pigment Yellow 109, C.I. Pigment Yellow 1 10, C.I. Pigment Yellow 1 13, C.I.

Pigment Yellow 1 14, C.I Pigment Yellow 1 17, C.I. Pigment Yellow 120, C.I.

Pigment Yellow 124, C.I Pigment Yellow 128, C.I. Pigment Yellow 129, C.I.

Pigment Yellow 133, C.I Pigment Yellow 138, C.I. Pigment Yellow 139, C.I.

Pigment Yellow 147, C.I Pigment Yellow 151 , C.I. Pigment Yellow 153, C.I. Pigment Yellow 154, Pigment Yellow 155, C.I. Pigment Yellow 167, C.I. Pigment Yellow 172 or C.I. Pigment Yellow 180.

[0037] Non-limiting examples of suitable magenta or red or violet organic pigments include C.I. Pigment Red 1 , C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 4, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 8, C.I. Pigment Red 9, C.I. Pigment Red 10, C.I. Pigment Red 11 , C.I. Pigment Red 12, C.I. Pigment Red 14, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 17, C.I. Pigment Red 18, C.I. Pigment Red 19, C.I. Pigment Red 21 , C.I. Pigment Red 22, C.I. Pigment Red 23, C.I. Pigment Red 30, C.I. Pigment Red 31 , C.I. Pigment Red 32, C.I. Pigment Red 37, C.I. Pigment Red 38, C.I. Pigment Red 40, C.I. Pigment Red 41 , C.I. Pigment Red 42, C.I. Pigment Red 48(Ca), C.I. Pigment Red 48(Mn), C.I. Pigment Red 57(Ca), C.I. Pigment Red 57:1 , C.I. Pigment Red 88, C.I. Pigment Red 112, C.I. Pigment Red 1 14, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. Pigment Red 168, C.I. Pigment Red 170, C.I. Pigment Red 171 , C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 179, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 187, C.I. Pigment Red 202, C.I. Pigment Red 209, C.I. Pigment Red 219, C.I. Pigment Red 224, C.I. Pigment Red 245, C.I. Pigment Violet 19, C.I. Pigment Violet 23, C.I. Pigment Violet 32, C.I. Pigment Violet 33, C.I. Pigment Violet 36, C.I. Pigment Violet 38, C.I. Pigment Violet 43 or C.I. Pigment Violet 50.

[0038] Non-limiting examples of blue or cyan organic pigments include C.I. Pigment Blue 1 , C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:34, C.I. Pigment Blue 15:4, C.I. Pigment Blue 16, C.I. Pigment Blue 18, C.I. Pigment Blue 22, C.I. Pigment Blue 25, C.I. Pigment Blue 60, C.I. Pigment Blue 65, C.I. Pigment Blue 66, C.I. Vat Blue 4 or C.I. Vat Blue 60.

[0039] Non-limiting examples of green organic pigments include C.I. Pigment Green 1 , C.I. Pigment Green2, C.I. Pigment Green 4, C.I. Pigment Green 7, C.I. Pigment Green 8, C.I. Pigment Green 10, C.I. Pigment Green 36 or C.I. Pigment Green 45.

[0040] Non-limiting examples of brown organic pigments include C.I. Pigment Brown 1 , C.I. Pigment Brown 5, C.I. Pigment Brown 22, C.I. Pigment Brown 23, C.I. Pigment Brown 25, and C.I. Pigment Brown , C.I. Pigment Brown 41 or C.I. Pigment Brown 42.

[0041] Non-limiting examples of orange organic pigments include C.I.

Pigment Orange 1 , C.I. Pigment Orange 2, C.I. Pigment Orange 5, C.I. Pigment Orange 7, C.I. Pigment Orange 13, C.I. Pigment Orange 15, C.I. Pigment Orange 16, C.I. Pigment Orange 17, C.I. Pigment Orange 19, C.I. Pigment Orange 24, C.I. Pigment Orange 34, C.I. Pigment Orange 36, C.I. Pigment Orange 38, C.I. Pigment Orange 40, C.I. Pigment Orange 43 or C.I. Pigment Orange 66.

[0042] In some examples, colorant particles may be dispersed in the carrier fluid. In one example, the colorant particles may be selected from pigment particles that are self-dispersible in the non-polar carrier fluid. It is to be understood, however, that non-dispersible pigment particles may otherwise be used so long as the electronic ink includes one or more suitable dispersants. Such dispersants include hyperdispersants such as those of the SOLSPERSE® series manufactured by Lubrizol Corp., Wickliffe, OH (e.g., SOLSPERSE ® 3000, SOLSPERSE ® 8000, SOLSPERSE ® 9000, SOLSPERSE ® 1 1200, SOLSPERSE ® 13840, SOLSPERSE ® 16000, SOLSPERSE ® 17000, SOLSPERSE ® 18000, SOLSPERSE ® 19000, SOLSPERSE ® 21000 or SOLSPERSE ® 27000); various dispersants manufactured by BYKchemie, Gmbh, Germany, (e.g., DISPERBYK® 1 10, DISPERBYK® 163, DISPERBYK ® 170 or DISPERBYK® 180); various dispersants manufactured by Evonik Goldschmidt GMBH LLC, Germany, (e.g., TEGO® 630, TEGO® 650, TEGO®651 , TEGO® 655, TEGO® 685 or TEGO® 1000); or various dispersants manufactured by Sigma-Aldrich, St. Louis, MO, (e.g., SPAN® 20, SPAN® 60, SPAN® 80 or SPAN® 85).

[0043] In some examples, an electronic ink may further include a surfactant. When used in an electronic ink, in some examples, surfactants may be colorless molecules that are dispersible or soluble in the carrier fluid of the electronic ink. In some examples, a surfactant may be present directly on the surface of a pigment particle or on a resin particle that contains a pigment. In such examples, the surfactant may create charge on the pigment or colorant particles, may carry counter charges that stabilize the ink, or may help prevent colorant particle aggregation.

[0044] In yet other examples, an electronic ink may further include a charge director. As used herein, the term "charge director" refers to a material that, when used, facilitates charging of the colorant particles. In one example, the charge director may be basic and may react with the acid-modified colorant particle to negatively charge the particle. In other words, the charging of the particle may be accomplished via an acid-base reaction (or interaction) between the charge director and the acid-modified particle surface. It is to be understood that the charge director may also be used in the electronic ink to prevent undesirable aggregation of the colorant in the carrier fluid. In other examples, the charge director may be acidic and may react (or interact) with the base- modified colorant particle to positively charge the particle. Again, the charging of the particle may be accomplished via an acid-base reaction (or interaction) between the charge director and the base-modified particle surface.

[0045] The charge director may be selected from small molecules or polymers that are capable of forming reverse micelles in the non-polar carrier fluid. Such charge directors may be colorless and may tend to be dispersible or soluble in the carrier fluid. In a non-limiting example, the charge director may be selected from a neutral and non-dissociable monomer or polymer such as, e.g., a polyisobutylene succinimide amine, which has a molecular structure as follows:

where "n" is selected from a whole number ranging from 15 to 100.

[0046] Another example of the charge director includes an ionizable molecule that is capable of disassociating to form charges. Non-limiting examples of such charge directors include sodium di-2-ethylhexylsulfosuccinate or dioctyl sulfosuccinate. The molecular structure of dioctyl sulfosuccinate is as follows:

[0047] Yet another example of the charge director includes a zwitterion charge director such as, for example, lecithin. The molecular structure of lecithin is shown as follows:

[0048] Finally, in some examples, the electronic ink may further include other additives such as optical brighteners, polymers, rheology modifiers, surfactants, viscosity modifiers or combinations thereof.

[0049] In some examples, the concentration of colorant particles and other additives, such as dispersants, charge directors, or surfactants, in the electronic ink, may range from about 0.5 to 20 percent by weight (wt%). In one example, the concentration of the colorant particles in the electronic ink may range from about 1 to 10 wt%. In such an example, the carrier fluid makes up the balance of the ink.

[0050] FIG. 2, on coordinates of relative intensity and time, illustrates in plot 200 the intensity of the light state over a set period of time of an electrokinetic device including inks with a magenta pigment and varying amounts of the oligomer disclosed herein. In the three trials, inks with a 0.03 molar (Curve 205), 0.0075 molar (Curve 215), and 0.015 molar (Curve 210) solution of a polyisobutene oligomer with a M_n of 1000 were tested by switching an electrokinetic device including the inks to a clear state, collecting data over a set period of time, and ending the experiment by forcing the device into a dark state. As seen in plot 200, all three trials with ink including polyisobutene oligomers showed consistent states of light intensity over time. Therefore, all three inks showed multi-stability properties, with the inks including higher concentrations of the polyisobutene oligomer having slightly better retention of the initial light state.

[0051] FIG. 3, on coordinates of relative intensity and time, illustrates in plot 300 the intensity of the light state over a set period of time of an electrokinetic device including inks with a black pigment and various kinds of the oligomers disclosed herein. In the trials, inks with a M_n of 6995 (Curve 310), 10000 (Curve 315), and 8012 (Curve 320), as well two typical non-polar carrier fluid without the oligomer disclosed herein, a high weight hydrocarbon fluid (Curve 325) and a petroleum hydrocarbon fluid (Curve 305), were tested. Again, the inks were tested by switching an electrokinetic device including the inks to a clear state, collecting data over a set period of time, and ending the experiment by forcing the device into a dark state. As seen in plot 300, the inclusion of the oligomers disclosed herein in an electronic ink allows the ink to have a consistently maintained high light intensity over time and therefore, multi- stability properties.

[0052] FIG. 4 is a depiction of an image 400 displayed in an electrokinetic device using an electronic ink including the oligomer described herein 40 minutes after the electrokinetic device has been removed from a power source. As seen in image 400, 40 minutes after the electrokinetic device has been removed from the power source, the image is still clearly visible, suggesting that the. electronic ink including the oligomer described herein has at least bi-stability properties or in other words, is capable of maintaining both the clear state and a single colored state after removal from a power source.

[0053] FIG. 5A is a depiction of an image 500a displayed in an electrokinetic device using an electronic ink including the oligomer disclosed herein and connected to a power source (not shown), and FIG. 5B is a depiction of an image 500b displayed in the same electrokinetic device as FIG. 5A 15 hours after the electrokinetic device has been disconnected from a power source. As seen in the image 500b 15 hours after the electrokinetic device has been removed from a power source, the image of the color gradient is still clearly visible, suggesting that the electronic ink including the oligomer described herein has multi-stability properties or in other words, is capable of maintaining multiple colored states after removal from a power source.

[0054] It should be understood that the foregoing multi-stable electronic inks including oligomers have been described with specific application to electrokinetic devices. However, such inks may find use in electrophoretic devices and other electro-optical devices as well.

Claims

CLAIMS What is claimed Is:

1. A multi-stable electronic ink including:

a non-polar carrier fluid;

a pigment particle; and

an oligomer having a number average molecular weight between 183 and 20,000, exclusive.

2. The electronic Ink of claim 1, wherein the oligomer !e selected from the group consisting of hydrocarbon polymers and siloxane polymers.

3. The electronic ink of claim 2, wherein the oligomer further includes any functional group.

4. The electronic ink of claim 1 wherein the non-polar carrier fluid Is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenatad hydrocarbons, slloxanee, and' combinations thereof.

5. The electronic Ink of daim 4 wherein the non-polar solvent is selected from the group consisting of perchloroethyiene, cydohexane, dodecane, cyclopentaslloxane, cydohexasiloxane, cydooctamethylslloxane, isoparafflnlo fluids, mineral oil, and combinations thereof.

6. The eledronio ink of daim 1 wherein the pigment partlde la selected from the group consisting of black pigment partldea. yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment partides, cyan pigment particles, blue pigment partides, green pigment partldea, orange pigment partides, brown pigment particles, and whits pigment particles.

7. The electronic ink of claim 6 wherein the pigment particle Is a colored polymeric partide having a size ranging from 10 nm to 10 pm.

8. The electronic ink of claim 1 further Induding e charge director, wherein the charge director Is a email molecule or polymer that Is capable of forming reverse micelles In the non-polar carrier fluid.

9. The electronic ink of dalm 1 further induding additional additives selected from the group consisting of optical brtghteners, polymers, rheotogy modifiers, surfactants, vtecosrty modifiers, and combinations thereof.

10. In combination, an electronic display and a multi-stable electronic ink, wherein the electronic display indudes;

a first electrode;

a second electrode; and

a display cell having a recess defined by a dielectric material, the first electrode, and the second electrode, the display cell containing the electronic Ink; and wherein the electronic ink Indudes:

a non-polar carrier fluid;

a pigment particle; and

an oligomer having a number average molecular weight between 183 and 20,000, exdusive.

1 .The combination of claim 10 wherein the electronic display Includes a plurality of display cells In a stacked configuration, associated first electrodes and second electrodes, and a plurality of electronic Inks of different colors, each display cell containing an electronic ink of a different color.

12. The combination of claim 10 wherein the oligomer further includes any functional group.

13. The combination of claim 10 wherein the non-polar carrier fluid is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially hatogenated hydrocarbons, sfloxanes, and combinations thereof.

14. The combination of claim 1 wherein the pigment particle has a size ranging from 10 nm to 10 pm and is selected from the group consisting of black pigment particles, yellow pigment particles, magenta pigment partldes, red pigment particles, violet pigment partldes, cyan pigment partides, blue pigment particles, green pigment partlcies, orange pigment parOdes, brown pigment particles, and white pigment partldes.

15. The combination of claim 10 wherein the electronlo Ink further indudes additives selected from the group consisting of a charge director, surfactants, optical brighteners, polymers, rheology modifiers, viscosity modifiers and combinations thereof, and wherein if the additive indudes a charge director, the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.